In developed and developing countries, primary treatment and disinfection of waste water discharges from collection systems and waste water treatment facilities is the first step to improving water quality. As the countries continue to advance, secondary and tertiary waste water treatment processes are added to provide additional treatment of the primary effluent.
Primary treatment removes large solids via screening and gravitational settling to remove light and dense solids, allowing neutrally buoyant matter to pass into the secondary treatment process or receiving body of water. Primary treatment utilizing gravitational settling or clarification is recognized as removing 20-33% of the organic load as measured in Biochemical Oxygen Demand (BOD). Secondary treatment removes another 50+% of the organic load by converting the BOD to biomass (bacteria) and CO2.
Secondary treatment provides an environment of adequate temperature, volume, mixing, and oxygen or the absence of oxygen in anaerobic processes to sustain the bacterial population necessary to consume the BOD and nutrients remaining in the waste water after primary treatment. New organic matter enters the treatment facility continuously so a portion of the existing bacterial population is removed from the process to promote the growth of new bacteria. The effectiveness of primary treatment directly affects the secondary process or the receiving body of water as discharged from the collection system.
In the parent application (U.S. Ser. No. 14/142,197) of the present invention, the effluent decanter is a screen decanter assembly in the form of a rectangular box (SBX) controllably driven in the vertical direction to optimize the exposure of the screen to the wastewater to varying wastewater levels. The. SBX can be lifted from the wastewater for backflushing and sterilization in a dedicated overhead apparatus. Because the motion of the effluent decanter is only vertical, the required footprint within the tank can be relatively small. A waste water treatment facility may comprise a ganged plurality of such vertically-driven effluent decanters for wastewater systems having high flows, limited surface area, and/or shallow active tank volumes. A tank for accommodating such a plurality typically has a V-shaped cross-section.
In the prior art, to avoid disturbing and re-suspending the settled organics, the effluent is brought out of the decanter by a hose connecting the bottom of the decanter to an outlet in the wall of the tank. The hose has several requirements that must be met for proper operation of the system.
First, it must maintain a solid connection with both the decanter and the tank wall as the water level and thus the decanter elevation changes through the operating cycle.
Second, it must fold into a compact space as the decanter reaches the bottom of its travel. For municipal water treatment plants, this space can often take the form of a “V” shaped trough which typically accommodates several decanters along its length.
Third, it must not contact the sides of the tank because this would both disturb the settled BOD sludge and potentially. damage the hose.
Fourth, the hose must be strong enough to support its own weight, even when suspended above the water surface and filled with water as can occur during maintenance or cleaning.
Fifth, the hose and connections must be highly reliable and possess long service and maintenance intervals because the nature of waste treatment is nearly 24/7 continuous operation for several years duration.
Sixth, the hose must have a constant volume at all hose positions and must remain substantially full of water or screened effluent at all times to prevent an uncontrolled inrush of fresh effluent into the decanter when the tank is refilled. Such an inrush risks immediate plugging of the decanter screens by solid materials which otherwise would float and be skimmed off or would settle before reaching the decanter.
In practice it is difficult for a flexible hose or rigid pipe or other alternative means to meet all of these requirements: a conventional prior art flexible hose, as disclosed in incorporated U.S. application Ser. No. 14/142,197, can contact the tank wall and may not be sufficiently strong to support its weight when filled with fluid; a telescoping pipe does not enable sufficient vertical range of travel of an SBX; and a tilting pipe, also as disclosed in U.S. application Ser. No. 14/142,197, requires the length of its tilt arm to pivot along the tank's horizontal axis and thus would reduce the possible number of decanters.
It is a principal object of the invention to provide a versatile and compact mechanism for meeting the above requirements while draining a vertically-driven or floating decanter over a wide range of influent and effluent flow rates.